1. Field of the Invention
This invention relates to an ink jet head unit for performing color printing by using a plurality of ink nozzle arrays each for use in printing one line, the plurality of ink nozzle arrays corresponding to a plurality of basic colors, and an ink jet printing apparatus incorporating the head unit.
2. Prior Art
Conventionally, an ink jet head unit of this kind was proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 10-95114. In this ink jet head unit, ink nozzle arrays each for use in printing one line are divided with respect to the direction along the line (by cutting each line in a direction crosswise to the direction along the line) into a plurality of divisional ink nozzle arrays, and ink jet heads are constituted by the divisional ink nozzle arrays, respectively. The plural ink jet heads formed as above are arranged in a manner staggered from each other on a support base, and each of them is fixed to the support base by two screws.
In the conventional ink jet head unit, since the ink nozzle arrays each for printing one line are divided to form the ink jet heads, the yield of the ink jet head unit can be improved. However, it is required to fix each of the plural ink jet heads onto the support base with precision, which makes it difficult to ensure positional accuracy between the ink jet heads.
It is an object of the invention to provide an ink jet head unit which is capable of incorporating a large number of ink jet heads with ease and precision, and an ink jet printing apparatus incorporating the ink jet head unit.
To attain the above object, according to a first aspect of the invention, there is provided an ink jet head unit for performing color printing by using a plurality of ink nozzle arrays each for use in printing one line, the plurality of ink nozzle arrays corresponding to a plurality of basic colors.
The ink jet head unit according to the first aspect of the invention is characterized by comprising:
a plurality of head groups each formed by a plurality of ink jet heads, and having the plurality of ink nozzle arrays arranged therein such that the plurality of ink nozzle arrays are divided among the plurality of head groups;
a plurality of sub-carriages having respective ones of the plurality of head groups mounted thereon; and
a unitizing carriage having the plurality of sub-carriages mounted thereon.
According to this ink jet head unit, a plurality of ink jet heads constituting each head group are mounted on a sub-carriages, and hence it is possible to mount the ink jet heads on the sub-carriage with relatively high accuracy. Further, a plurality of sub-carriages thus constructed are mounted on a unitizing carriage. This makes it possible to mount all the ink jet heads on the unitizing carriage with relatively high accuracy. In short, by ensuring positional accuracy between each individual ink jet head and a corresponding one of the sub-carriages as well as between each sub-carriage and the unitizing carriage, it is possible to ensure a high mounting accuracy between each ink jet head and the unitizing carriage. Therefore, it is possible to mount a large number of ink jet heads on the unitizing carriage with precision, without any need to directly consider positional accuracy between the individual ink jet heads and the unitizing carriage.
It should be noted that the term xe2x80x9cone linexe2x80x9d mentioned above means xe2x80x9ca line of dots corresponding to a sequence of ink nozzles on the head unit substantially corresponding to a printing width in a sub scanning directionxe2x80x9d. The term is intended to include a line of dots corresponding to a combination of divisional ink nozzle arrays, referred to hereinafter, and further, a line of dots in the case where the combination of divisional ink nozzle arrays are arranged in the sub scanning direction in an overlapping fashion. However, it is not intended to mean the width of a print medium.
Preferably, the plurality of ink nozzle arrays are each divided into a plurality of divisional ink nozzle arrays with respect to a direction along the one line, and are grouped into a plurality of divisional ink nozzle array groups each formed of corresponding ones of the plurality of divisional ink nozzle arrays, and the plurality of ink jet heads of each of the plurality of head groups have the plurality of divisional ink nozzle arrays of a corresponding one of the plurality of divisional ink nozzle array groups arranged therein such that the plurality of divisional ink nozzle arrays are divided among the plurality of ink jet heads.
According to this preferred embodiment, each divisional ink nozzle array group is formed by a plurality of ink jet heads and mounted on an associated sub-carriage. Therefore, it is possible to intensively arrange the (divisional) ink nozzle arrays of the basic colors. This makes printing, especially, color matching printing less susceptible to the accuracy or inaccuracy of the moving position of the head unit in the main scanning direction, so that it is possible to prevent degradation of print quality due to displacement of dots.
Alternatively, the head groups may be constructed such that each of them has ink nozzle arrays of a corresponding one of the basic colors.
Preferably, the plurality of sub-carriages are arranged in a manner staggered from each other on the unitizing carriage.
According to this preferred embodiment, the plurality of sub-carriages can be more intensively arranged on the unitizing carriage. Therefore, the unitizing carriage can be made compact in size, and a large number of ink jet heads can be intensively arranged.
More preferably, each of the ink jet heads comprises a head base plate, and a head body arranged in one substantial half of the head base plate toward one longitudinal side, the head body having a corresponding portion of the plurality of ink nozzle arrays arranged therein, and in each two of the plurality of head groups, adjacent to each other with respect to a direction along the line, the head body of each of the plurality of ink jet heads of one of the two head groups and the head body of each of the plurality of ink jet heads of another of the two head groups are arranged opposed to each other in a back-to-back fashion.
According to this preferred embodiment, the ink jet heads can be arranged further intensively.
Preferably, the plurality of ink jet heads are bonded to a corresponding one of the plurality of sub-carriages in a positioned state.
According to this preferred embodiment, each ink jet head is positioned on a corresponding one of the sub-carriages e.g. by using a jig and then fixedly bonded to the same. Therefore, differently from the case of fixing the ink jet heads by screws or the like, it is possible to effectively prevent positional displacement of the ink jet head. Moreover, this facilitates the work of fixing each ink jet head onto a sub-carriage.
Preferably, the unitizing carriage has a plurality of positioning pin groups provided on a surface thereof, for enabling each of the plurality of sub-carriages to be mounted in a positioned state, and each of the positioning pin groups positions a corresponding one of the plurality of sub-carriages on the unitizing carriage, with reference to a reference position set to a position of an outermost ink nozzle of an arbitrary one of the plurality of ink jet heads mounted on the corresponding one of the plurality of sub-carriages.
According to this preferred embodiment, in positioning each sub-carriage on the unitizing carriage, the position of the outermost ink nozzle of an ink jet head is set to a reference position for positioning the sub-carriage. Therefore, it is possible to minimize influence of positioning error between the sub-carriages and the unitizing carriage. Further, since the sub-carriages are each removable from the unitizing carriage, replacement of the sub-carriages is facilitated.
More preferably, the each of the positioning pin groups comprises a reference pin arranged in a manner corresponding to the reference position, an angle-limiting pin for positioning the corresponding one of the plurality of sub-carriages in a direction of rotation thereof about the reference pin on the unitizing carriage, an X-axis direction urging pin for urging the corresponding one of the plurality of sub-carriages in an X-axis direction toward the reference pin to thereby position the corresponding one of the plurality of sub-carriages in a Y-axis direction perpendicular to the X-axis direction, and a Y-axis direction urging pin for urging the corresponding one of the plurality of sub-carriages in the Y-axis direction toward the reference pin to thereby position the corresponding one of the plurality of sub-carriages in the X-axis direction.
According to this preferred embodiment, so long as excellent positional accuracy between the reference position, the reference pin and the angle-limiting pin is maintained, it is possible to fix (mount) the sub-carriage onto the unitizing carriage with ease and precision. Further, although the sub-carriages are made removable from the unitizing carriage, positioning accuracy cannot be spoiled.
To attain the above object, according to a second aspect of the invention, there is provided an ink jet printing apparatus incorporating the ink jet head unit according to the first aspect of the invention.
According to this ink jet printing apparatus, the positional accuracy between the plurality of ink jet heads and the unitizing carriage can be maintained, and hence it is possible to accurately arrange the ink nozzle array groups for printing lines of basic colors of ink. Further, since a faulty ink jet head can be replaced with a new one as required, it is possible to improve the yield of the ink jet head unit.
Preferably, the ink jet printing apparatus includes an X-Y moving mechanism for moving the ink jet head unit in a main scanning direction and a sub scanning direction, and the ink jet printing apparatus performs printing by causing the ink jet head unit to scan on a print medium in the main-scanning direction and the sub-scanning direction.
According to this preferred embodiment, print quality can be enhanced by constructing the X-Y moving mechanism with accuracy. Further, it is possible to minimize position-shifting operation of the ink jet head unit, thereby increasing the printing speed.
Preferably, the ink jet printing apparatus further includes a cleaning cap unit for sucking ink from the ink jet head unit, in a state held in intimate contact with the ink jet head unit, and the cleaning cap unit has a plurality of caps for intimate contact with the ink jet head unit, each of the plurality of caps having a size large enough to enclose at least one of the plurality of ink jet heads.
According to this preferred embodiment, by operating the X-Y moving mechanism, the ink jet head unit can be cleaned on an ink jet head(s)-on-ink jet head(s) basis. Therefore, it is possible to make the cleaning cap unit compact in size without causing any inconvenience of cleaning operation for the ink jet heads.
Preferably, the ink jet printing apparatus further includes a storage cap unit for being brought into intimate contact with the ink jet head unit to thereby seal ink nozzles of the plurality of ink nozzle arrays, and the storage cap unit is formed to have a size large enough to receive all of the ink jet heads of the ink jet head unit.
According to this preferred embodiment, it is possible not only to carry out excellent flushing of all the ink nozzles, but also to effectively prevent the ink nozzles from being dried up during storage. Further, since all the ink jet heads are collectively sealed by the single storage cap, manufacturing costs can be reduced, differently from a case in which a plurality of contact caps are provided for intimate contact with the respective heads. Further, since the storage cap and the cleaning cap are separately constructed, it is possible to reduce stain or dirt deposited on the ink head unit via the intimate contact caps.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.